The Large Hadron Collider: building the world’s most complex experiment

Jessica Rowley

The LHC is the world’s largest and most complex experiment. How do you build a piece of experimental kit that has never been built before, to look for something that might not exist? And – more importantly – why build it? Lyn Evans and Chris Allton were invited to explain, in conversation with Sue Nelson, during a session at this year’s British Science Festival. Alan Barker was there to hear their answers.

If you’re a scientist speaking at a science festival – and perhaps particularly if you work in particle physics – you need to be ready to answer two kinds of question. Lyn Evans and Chris Allton were faced with both during a session at the British Science Festival in Swansea. Lyn is director of the Linear Collider collaboration at CERN, and had previously worked as project leader on the Large Hadron Collider (or LHC). Professor Allton works at the Department of Physics at Swansea University; his interest in quarks brings him into close collaboration with the LHC.

Summarise the first question as: “What use is all this?” Sue Nelson asked Evans: “Is the science worth it?” His reply was an unequivocal “absolutely.” Not only does the LHC provide great science, but it also pushes the frontiers of technology; it’s an example of international collaboration on a massive scale; and it’s inspiring young people to go into the hard sciences. He’s personally involved in a project bringing science teachers from Wales to CERN, helping to spread the word.

Evans knows all about justifying expensive science projects. The LHC began as a dream in the 1980s. First came the need to build an international consensus that the experiment was necessary; then the design stage, complete with all-important cost estimates; and then a campaign to convince the public and their political representatives to fund it. By 1994, they were ready to start building. Fifteen years later, the machine was operational. Even then, scare stories about triggering the end of the world fuelled a frenzy of speculation – especially on social media – so that, when the LHC was finally switched on in 2008, Eurovision broadcast the event to 1.5bn people.

The next task is to explain to the public what the machine does. Allton supplied an analogy. Imagine investigating how a bicycle works: you can use spanners to take it apart. But if you want to know how a proton works, nature hasn’t supplied any spanner small enough. The only option is to smash two protons together and look at what emerges. Imagine smashing together two bicycles and then trying to interpret the mess. That, explained Allton, is more or less what the scientists at the LHC are trying to do.

Evans slipped seamlessly from bicycles to oranges. You’re looking for the pips, but you have to sort through a mass of pulp. The need to process unimaginably large amounts of data led, in 1989, to Tim Berners Lee inventing the World Wide Web – one of the prime candidates for top practical application to emerge from the LHC. Evans is now working on the Grid, a global collaboration linking more than 170 computing centres in 42 countries, which will provide the resources to process the 30 petabytes (30 million gigabytes) of data that the LHC generates each year.

Crunching data 24/7 hasn’t quite the thrill of finding a new boson, or, alternatively, destroying fifty megamagnets in one accident – an especially low point in Lyn Evans’ career. But the LHC’s ongoing work will help scientists understand the Higgs boson’s properties, and also – perhaps – discover particles as yet unknown. The ‘pulp’ data, on repeated runs of the machine, will tend to flatten out, allowing the tell-tale signal of a new particle to spike. And then, we need to understand what Evans calls the subtle asymmetry between matter and anti-matter. At the moment of the Big Bang, they should have cancelled each other out, leaving a universe flooded with nothing by light. But they didn’t, and we exist. How has that come about?

Such questions bring physicists dangerously close to the second kind of tricky science festival question. What does it all mean? Allston had earlier justified pure research in humanistic terms: the discovery of the Higgs boson was like a work of art, he said, enriching society because it enriches us as human beings. But these are perilous quicksands for hard scientists. The discoveries at LHC have contributed to a penumbra of speculation, ranging from the philosophical to the mystical, about the nature of reality. The Higgs boson itself, for example, was very quickly labelled ‘the God particle’ – a phrase that both Evans and Allston find embarrassing.

Towards the end, Evans hinted at the pursuit of knowledge as something more than intellectual. We understand only about 5% of the universe; 95% is made up of dark matter and dark energy, about which we know nothing. “And that,” he said quietly, “is an unacceptable situation.”

Alan Barker, Swansea British Science Festival, September 2016. Alan Barker is a writer and training consultant specialising in communication skills. He is Managing Director of Kairos Training Limited.

One of our CREST Youth Panel members, Floriane Fidegnon, was lucky enough to be the youth speaker at the Grand Challenges Conference, hosted by the Bill and Melinda Gates Foundation. Here she spills all about the experience and has an important message for scientists and researchers...